*{
  box-sizing: border-box;
}

.box1{
  width: 100px;
  height: 100px;
  background: url('./1.jpg') center no-repeat;
  background-size: 100% 100%;
}

.box2{
  width: 200px;
  height: 200px;
  background: url('./2.jpg') center no-repeat;
  background-size: 100% 100%;
}

.box3{
  width: 300px;
  height: 300px;
  background: url('./3.jpg') center no-repeat;
  background-size: 100% 100%;
}